Writing instruments, and specifically pencils, have been in widespread use for hundreds of years, with mechanical pencils dating as far back as the 18th century. With the advent of mechanical pencils, a pencil could be used continuously by simply refilling the modular lead housed in the body. A variety of different mechanical pencil configurations are known in the art including various mechanisms for retaining and advancing lead or other writing mediums within the writing instrument. In general, mechanical pencils expose the lead for writing by driving it forward when a knock button is pressed. The knock button may be disposed on the end of the pencil, or on the side. Generally at rest, the lead is selectively fixed by a split chuck or similar gripping mechanism that cooperates with the lead tube to hold the lead and deliver it to the writing tip of the writing instrument. Upon the actuation of the knock button, the mechanism cycles, a process which includes advancing the lead tube, which increases the force exerted by a return element on the lead tube, which opens the chuck, and allows the lead tube to walk back with respect to the lead without moving the lead.
In conventional side-knock configurations, any slight rotation of the lead tube with respect to the knock button must be prevented during actuation in order to ensure that the knock button properly aligns with the feature on the lead tube to completely cycle the mechanism. Rotation of the lead tube in such a conventional side-knock style writing instrument can cause undesirable misalignment of the knock button and the lead tube feature that can result in failure of the mechanism to cycle, meaning failure of the tube to advance, or result in reduced actuation distance that impairs lead delivery to the writing tip of the instrument.
Conventional side-knock writing instruments typically include a guide structure either on the barrel, the lead tube, or both, to prevent such rotation. Guides can include grooves on the barrel or cooperating structures between the lead tube and the barrel that prevent rotation during actuation. This adds complexity and cost to the manufacture of the writing instruments. Such additional structures must be aligned during assembly of the writing instrument and provide yet another source of potential error during the manufacturing process. The guide structures and complexity added can also increase problems with use or breakage of the writing instrument or lead during use, if the guide structure fails or breaks.
Accordingly, a need exists to create a simple, reliable, side-knock mechanism for mechanical pencils that overcomes one or more of the disadvantages of current designs.